This invention in general relates to fiber optic communications systems and in particular to the structure of connectors for joining optical fibers and to methods by which such connectors can be fabricated.
The use of optical fibers as a medium for transmitting high volumes of information over both long distances and throughout local area networks is now a well-established practice known throughout the communications industry.
Optical fibers are hair-like filaments of glass typically having a central region of high index of refraction surrounded by a sheath or cladding region of lower index, a structure which causes optical radiation properly injected into the fiber to propagate along its length and emerge from its distant end.
Although size and information carrying capacity are fundamental reasons responsible for the attractiveness of optical fiber for communications purposes, they are equally reasons underlying the difficulties associated with splicing and connecting fibers wherever required in a communications system. The scale of optical fibers demands high precision in axial, lateral, and angular alignment, and the penalty for lack of precision is large signal loss.
Consequently, the major problems surrounding connectors, i.e., devices by which fibers or bundles of fibers can be coupled and uncoupled some reasonable number of times, are concerns with hardware capable of alignment to a high degree of accuracy, whether mechanical or optical.
The technical problems associated with connectors, along with economic considerations, have required those skilled in the art to pursue solutions along several different lines, each approach with its relative merits. These approaches have resulted in three general types of connector - the groove type, the ferrule type, and the lens type.
With the groove type, the surface of a precision block is provided with fine V-grooves into which the fibers to be aligned are laid and clamped. Coupling of two cable ends is completed by bringing the blocks into accurate alignment so that corresponding cores of the fibers in the V-grooves line up with one another.
In the ferrule type, precision ground ferrules are fitted around the ends of fibers and an alignment system is arranged to align the ferrules which, in turn, align the fiber cores.
The lens type of connector attempts to reduce the tolerance requirements on alignment by increasing the apparent size of the fibers so that alignment is of enlarged images of fibers rather than the fibers themselves. This still, however, requires accurate alignment of the fibers with respect to the lens and of the lens to another to complete the connection.
A known solution to the problems associated with the lens connector approach is to use a connector that is injection molded of one plastic piece in which all the precision required is provided for by way of the molding tools and the process for fabricating the piece. Such connectors are referred to as expanded beam types and are of the sort described in U.S. Pat. Nos. 4,183,618; 4,186,995 and 4,421,383. However, injection molding connectors of the scale and precision required is not without challanges as those skilled in the art will appreciate. Consequently, it is a primary object of the present invention to provide the art with a simple lens-type connector which can be easily fabricated.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter. The invention, accordingly, comprises the fabrication techniques and the apparatus possessing the construction, combination of elements, and arrangement of parts exemplified in the detailed disclosure which follows.